The present invention relates to color change systems for spray coating apparatus, and in particular to a color change valve structure for use with a rotary head electrostatic spray coating system, which enables the system to be rapidly and thoroughly cleansed of coating material of one color in preparation for spraying coating material of another color.
Electrostatic spray coating systems have been successfully used in commerce in several different forms. For example, systems have been used in which spraying or atomizing devices employ hydraulic forces or air as the atomizing medium, and means are provided for electrostatically charging the spray particles for attraction to articles or ware to be coated. In another type of system, and with which the present invention is particularly suited for use, atomization is accomplished by means of a centrifugal sprayer member or head to which a rapid rotation is imparted. The head has a surface against which a stream or jet of liquid to be sprayed is directed through an orifice, the liquid on striking the revolving surface progressing radially outwardly thereover in a thin film under centrifugal force toward a sharp annular peripheral edge of the head, whereat it is divided into fine particles so that it leaves the periphery in the form of a spray. For electrostatic deposition of coating material the rotary head is made of a conductive material and connected to a high d.c. potential, so that the spray particles on moving past the peripheral edge of the head are charged to a high electrostatic potential. The resulting ionized or electrostatically charged cloud of particles is then attracted to and settles on the surface of articles to be coated, which are maintained at a different and usually ground potential.
In use of such electrostatic spray coating systems, it often happens that articles are required to be coated a wide variety of colors. In such a case, it is generally not practical to establish separate spray stations or production lines for each color, or even to spray a long sequence of articles of one color, then another long sequence of articles of a second color, etc. Instead, it is desirable to be able to make color changes rapidly and simply at a single spray station.
Color change systems are useful in such cases, and enable a variety of colors to be sprayed from a single spray coating apparatus. In one conventional color changer, for example, a plurality of supply containers of coating material, each of a different color and having a separate motor driven fluid pump, are connected with a manifold through valve controlled ports. An outlet from the manifold connects through a supply line with an inlet to the spray coating apparatus, and to spray material of a particular color the port valve associated therewith is opened and the motor driven pump for the supply is energized to provide the fluid through the manifold and supply line to the spray coating apparatus inlet, and thence to the orifice for impingement against the rotary head. After completion of spraying coating material of a particular color, the manifold, supply line and spray coating apparatus are cleansed with flushing media to prepare the same for spraying material of a different color.
Preparing conventional electrostatic spray coating systems to spray a new color of coating material has heretofore involved a rather exacting process, primarily because the entirety of the supply line and the spray coating apparatus must be cleansed of material. To accomplish the same, flushing media is introduced through the supply line, and with conventional spraying apparatus the entirety of the flushing media is discharged through the orifice and against the rotary head. Consequently, not only is the flow rate of the flushing media restricted to the extent that it must pass through the orifice, but also the flushing media is emitted from the head in a spray, and some means must be provided to prevent it from freely entering and polluting the atmosphere and depositing on articles. One such means contemplated by the prior art is to place an enclosure around the rotary head during a color change operation, and another to move the entirety of the spray coating apparatus to a position whereat the sprayed flushing media may be properly contained. In either case, the color change process is complex and time consuming.